1. Field of the Invention
The present invention relates to a polymer composite comprising a three dimensional network structure formed from an organic polymer and a clay mineral, as well as a stretched product thereof, and production processes for such a polymer composite and stretched product.
2. Description of Related Art
Examples of long-known polymer composite materials, produced by complexing an organic polymer with an inorganic material, include materials produced by filling an organic polymer with not only glass fiber and carbon fiber, but also with talc, calcium carbonate or the like. In recent years, significant improvements in mechanical properties and thermal characteristics have been achieved by dispersing and complexing nanometer-scale, ultra-fine inorganic components within organic polymers, and these composite materials are attracting considerable interest as organic-inorganic nanocomposite materials.
The most commonly used inorganic components for these nanocomposite materials are metal oxides synthesized using sol-gel reactions, and clay minerals that can be exfoliated to form sheet-like layers (for example, see K. Haraguchi et al., J. Mater. Sci., 33, 3337-3344 (1998), and A. Usuki et al., J. Mater. Res., 8, 1174-1178 (1993)).
Of the proposed materials, nanocomposite materials that use clay minerals as the inorganic component benefit from the large aspect ratio of the layered clay, enabling good improvements to be achieved in both the mechanical properties and the gas shielding properties of the composite material. In these composites of clay minerals and organic polymers (nanocomposites), achieving a fine dispersion of the clay layers within the organic polymer, and maximizing the interaction between the clay layers and the organic polymer are both important factors. Accordingly, the organic polymer is often modified with maleic anhydride or oxazoline, and rather than selecting an inorganic clay mineral which is cheap but which does not disperse readily within the organic polymer, the clay mineral is often first treated with alkylammonium cations or the like, which widens the distance between layers and promotes easier interlayer exfoliation, and also improves the dispersion properties within organic solvents and organic polymers (whereas untreated clay is described as inorganic clay, this type of treated clay is referred to as organized clay).
Until now, these polymer composite materials known as nanocomposites have been prepared by complexing an organic polymer such as a polyamide, polystyrene, polypropylene, polyimide or polyurethane with organized clay. Because the thus produced polymer composites comprise a fine dispersion of clay layers with a large aspect ratio, improvements in properties such as the elastic modulus, the thermal deformation temperature, the gas permeability, and the burning rate have been reported (for example, see T. J. Pinnavaia and G. W. Beall Eds., Polymer-Clay Nanocomposites, Wiley (published 2000).
From the viewpoint of improving the performance of the polymer composite, larger quantities of clay mineral are desirable, although it is also important to achieve the maximum level of performance improvement with as small a quantity of clay mineral as possible. Based on the research to date, the quantity of clay is typically within a range from 0.2 to 5% by weight, and neither low inorganic content polymer composites with a clay content of less than 0.2% by weight, or particularly less than 0.1% by weight, nor high inorganic content polymer composites with a clay content more than 10% by weight, or particularlly exceeding 15% by weight are currently being used. This is because if the inorganic content becomes too low, then the performance improvements become almost unnoticeable, whereas if the inorganic content is too high, then the viscosity during production increases considerably, which can make it impossible to achieve the required level of nanoscale, ultra-fine, and uniform dispersion in the composite product, the moldability of the composite material deteriorates markedly, which can prevent the uniform molding of a desired shape, and the composite material also becomes more brittle, causing a significant deterioration in the mechanical properties (such as the strength and elongation).
As a result, the development of polymer composites which allow effective improvements in performance even if the clay mineral content is low, and polymer composites which display a uniform, ultra-fine dispersion of the inorganic component and offer superior mechanical properties even if the clay mineral content is high has been keenly sought.
The inventors of the present invention have previously developed a polymer hydrogel comprising a three dimensional network structure of an acrylamide based monomer and a water swelling clay mineral, and have reported that the resulting gel displays a variety of specific properties (American Chemical Society “Macromolecules” 2002, vol. 35, pp 10162 to 10171). This polymer hydrogel displays particularly superior levels of stretchability and strength when compared with conventional hydrogels formed using organic cross linking agents, and is consequently potentially useful, although if the water content falls, then the mechanical toughness deteriorates, and if the water content decreases to substantially zero, then the elongation of the material essentially disappears, resulting in a brittle material.